Material Properties of TiO2 Nanotube Arrays: Structural, Elemental, Mechanical, Optical and Electrical

  • Craig A. Grimes
  • Gopal K. Mor


In this chapter, we examine the structural, elemental, crystallization, optical, electrical, and mechanical properties of the anodization-synthesized titania nanotube arrays.

It is known that the as-fabricated nanotube arrays have an amorphous crystallographic structure. Upon annealing at elevated temperatures in an oxygen ambient, the nanotube walls transform into anatase phase, and a layer of metal underneath the nanotubes converts into rutile [1–9]; the observed crystalline phases are polycrystalline. We make note of a publication where the authors mistook the diffraction pattern of a selected small area, determined using transmission electron microscopy (TEM), as representing a single-crystal nanotube [10]. Titania properties depend on the crystallinity and isomorph type, and hence the utility of their application also varies. For example, anatase phase is preferred in charge-separating devices such as dye-sensitized solar cells (DSCs) and in photocatalysis, while rutile is used predominantly in gas sensors and as dielectric layers. Of the titania polymorphs, rutile has minimum free energy, and hence given the necessary activation energy, other polymorphs including anatase transform into rutile through a first-order phase transformation. The temperature at which metastable anatase converts to rutile depends upon several factors including the presence of impurities, feature size, texture, and strain. Hence with sintering, porosity and/or surface area reduction occur due to nucleation-growth type of phase transformations [11–13].


Barrier Layer Anatase Phase Flat Band Potential Barrier Layer Thickness Schottky Plot 
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Copyright information

© Springer Science + Business Media, LLC 2009

Authors and Affiliations

  1. 1.Electrical Engineering DepartmentPennsylvania State UniversityUniversity ParkUSA
  2. 2.Materials Research InstitutePennsylvania State UniversityUniversity ParkUSA

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